Recovery of nickel in soluble form from a liquor

ABSTRACT

A process for recovering nickel that is in soluble form and in relatively low concentrations, typically up to 2% by weight in a liquor, comprises: (a) precipitating nickel from solution (preferably as a hydroxide or sulphide); (b) adding an inert particulate carrier and a flocculent to the liquor to form flocs comprising nickel precipitate, inert particulate carrier, and flocculent; (c) separating the flocs from the liquor (preferably by gravitational settling or magnetic separation); and (d) separating the nickel precipitate from the flocs (preferably by agitating the flocs). The nickel precipitate and flocs are preferably then passed through a filter to remove the nickel as filter cake. The inert carrier is preferably sand, alumina, magnetite, hematite, ilmenite or calcite. The flocculent is preferably a cationic, non-ionic or anionic flocculent.

The present invention relates to a process for recovering nickel that isin soluble form in a liquor.

In many instances, the liquor from a leaching or beneficiation circuitfor oxidised nickel-containing ore contains nickel in dissolved form inrelatively low concentrations, typically up to 2% by weight. Thepreferred known method of recovering valuable species, such as nickel,that is in low concentrations in a liquor is to precipitate the valuablespecies and to pass the liquor through a thickener/filtration circuit toseparate the valuable species from the liquor. However, this is not asatisfactory solution for nickel because the nickel precipitates thatcan be formed most readily, such as nickel hydroxides and sulphides, aregelatinous and difficult to thicken and filter. In particular, thenickel precipitates tend to blind filters quickly. As a consequence,invariably the dissolved nickel is not received from the liquor.

An object of the present invention is to provide a cost-effectiveprocess for recovering nickel in soluble form from a liquor.

According to the present invention there is provided a process forrecovering nickel in soluble form from a liquor, the process comprising:

(a) precipitating nickel from solution;

(b) adding an inert particulate carrier and a flocculent to the liquorto form flocs comprising nickel precipitate, inert particulate carrier,and flocculent;

(c) separating the flocs from the liquor; and

(d) separating the nickel precipitate from the flocs.

It is preferred that the process further comprises passing the nickelprecipitates and flocculent through a filter to recover the nickel as afilter cake.

It is preferred that the precipitation step (a) comprises adjusting thepH of the liquor to precipitate the nickel as an hydroxide.

Alternatively, it is preferred that the precipitation step (a) comprisesadding sulphur containing compounds to precipitate the nickel as asulphide.

It is preferred that the separation step (c) comprises allowing theflocs to settle by gravity and separating the relatively clarifiedliquor from the flocs.

In an alternative form of the invention it is preferred that theseparation step (c) comprises recovering the flocs by a magneticseparator.

It is preferred that the separation step (d) be carried out by agitatingthe flocs.

The term "inert" as used herein in relation to "particulate carrier" isunderstood to mean that the particulate carrier is not substantiallyattacked by the liquor. In other words, the term "inert" means that theparticulate carrier exhibits both suitable chemical and physicalstability in the liquor.

It is preferred that the inert particulate carrier be selected from thegroup consisting of sand, alumina, magnetite, hematite, ilmenite andcalcite.

It is preferred that the flocculent be a polyelectrolyte flocculent. Theterm "polyelectrolyte flocculent" as used herein is understood to meanany suitable cationic, non-ionic and anionic flocculent.

The present invention is described further with reference to theaccompanying drawings in which:

FIG. 1 is a flow sheet of the main steps in a preferred embodiment ofthe process of the present invention; and

FIG. 2 is a flow sheet of the main process steps in a pilot plant trialof the process of the present invention.

With reference to FIG. 1, in a preferred embodiment of the process ofthe invention, a liquor from a leaching or beneficiation circuit forsoluble oxidised nickel-containing ore is conditioned in a series oftanks by pH adjustment or addition of a suitable sulfur-containingcompound to precipitate the nickel as an hydroxide or sulphide.

The resultant liquor containing a suspension of the nickel precipitate,an inert particulate carrier, and a polyelectrolyte flocculent are mixedtogether in a suitable form of mixing vessel in amounts selected to formflocs of the nickel precipitate and the inert particulate carrier.

The flocs and a relatively small part of the liquor are then separatedfrom the major part of the liquor by allowing the flocs to settle undergravity of directing the liquor in a stream pat a magnetic separator sothat the flocs are recovered on the magnetic separator.

The separated flocs and the relatively small part of the liquor areagitated to break-up the flocs and thereby separate the inertparticulate carrier and the nickel precipitate. The inert particulatecarrier is returned for re-use in the circuit described above and thenickel precipitate and remaining liquor are transferred to a suitablefilter or concentration system in with the nickel precipitate isseparated from the remaining liquor. Specifically, the nickelprecipitate is collected as the filter cake or consolidated sludge andthen is treated as required to recover the nickel values.

The preferred embodiment of the process of the invention described abovehas been found to be an efficient and effective process for recoveringsoluble nickel that is in low concentrations, typically less than 2 wt.%, in a liquor from a leaching or beneficiation circuit for oxidisednickel-containing ores.

The present invention is described further with reference to thefollowing examples.

EXAMPLE 1

A synthetic nickel-containing liquor was prepared to simulate a liquorfrom a nickel leaching circuit and was treated in accordance with thepreferred embodiment of the method the present invention.

The liquor was acidic and on neutralization to pH 8-8.5 produced a greengelatinous precipitate of nickel hydroxide. The neutralized liquor wasmixed with 10 vol % silica sand and a polyelectrolyte flocculent and theflocs of nickel hydroxide and silica sand were allowed to settle. Aftera suitable period of time, the flocs (with a part of the liquor) wereseparated from the relatively clarified liquor. The flocs were agitatedto break-up the flocs into a component comprising the silica sand and acomponent comprising the nickel hydroxide and the retaining liquor. Thenickel hydroxide/retained liquor component was separated from the silicasand component and was passed through a filter to separate the nickelhydroxide and the retained liquor.

It was found that the concentration of nickel hydroxide in the liquorwas significantly reduced by the preferred embodiment of the method ofthe present invention. Specifically, the concentration of nickelhydroxide dropped from 2000 mg/l to 10.5 mg/l.

In addition, it was found that the nickel hydroxide precipitate did notblind the filter.

EXAMPLE 2

A 13 day pilot plant trial was carried out on tailings dam water of theKwinana Nickel Refinery in Western Australia.

The tailings dam water containing dissolved nickel, copper, and cobalt,and suspended solids in the concentrations set out below.

    ______________________________________                                                    Concentration                                                                 Mg/l                                                              ______________________________________                                        Ni:           410-500                                                         Cu:           20-30                                                           Co:           40-70                                                           Suspended       20-18400                                                      solids:                                                                       ______________________________________                                    

The pH of the tailings dam water varied between 5.4 and 8.5.

The objective of the trial was to precipitate the nickel, copper andcobalt as metal sulphides and to remove the black metal sulphidesprecipitate and the suspended solids as a combined sludge.

The pilot plant was operated to treat between 3.4 and 3.8 m³ /hrtailings dam water during the course of the trial. Sodium sulphide wasadded to the tailings dam water as the sulphur-containing compound forprecipitating the nickel, copper, and cobalt from solution, alum wasadded as a coagulant, and magnetite was added as the inert particulatecarrier.

The pilot plant was operated in accordance with the sequence of steps inthe flow sheet shown in FIG. 2.

With reference to the figure, sodium sulphide (sulphide precipitant) andalum (coagulant) were added to the raw feed of tailings dam water andthe raw feed was then passed through a series of conditioning tanks 3 toallow sufficient residence time, typically 90 seconds, for the metalsulphide precipitate to form.

The raw feed, now containing a black gelatinous metal sulphideprecipitate, was transferred to an agitated tank 5 and mixed withmagnetite.

The agitated mixture was discharged continuously from the agitated tankand a flocculent was added to the mixture prior to introducing themixture into a conical constant density tank 7 having a central drafttube with a flocculent blending agitator located in the draft tube. Themixture was fed to the top of the draft tube and flocs of the metalsulphide precipitate/suspended solids/magnetite settled quickly to thebottom of the tank.

The underflow from the constant density tank 7 was transferred to acyclone 9 to separate the magnetite from the metal sulphide precipitate,suspended solids, and retained liquor. The magnetite, discharged as thecyclone underflow, was recycled to the agitator tank 5. The cycloneoverflow, which comprised the metal sulphide precipitate/suspendedsolids/retained liquor was transferred to a settling tank 11 in whichthe metal sulphide precipitate and suspended solids formed a concentrateof a toothpaste-like consistency.

The overflow from the constant density tank 11, which comprisedrelatively clarified liquor, was treated in a second series of agitatorand constant density tanks 13, 15 to remove any remaining metal sulphideprecipitate and suspended solids. The treated liquor discharged as theoverflow from the second constant density tank 15 was then analysed.

It was found from analysis of the treated liquor that the processconsistently removed in excess of 98% of the dissolved nickel, cobalt,and copper in the raw feed, with the treated liquor containing thefollowing concentrations of nickel, cobalt, copper and suspended solids.

    ______________________________________                                                    Concentration                                                                 Mg/l                                                              ______________________________________                                        Ni:           <5                                                              Cu:           <1                                                              Co:           <1                                                              Suspended     20-40                                                           solids:                                                                       ______________________________________                                    

The clarity of the treated liquor was excellent and all sampled testedwere 1 NTU or less when compared with deionised water.

In summary, the pilot plant trial established that the process of thepresent invention could remove efficiently and consistentlysubstantially all the dissolved nickel in the tailings dam water of therefinery.

Many modifications may be made to the preferred embodiments withoutdeparting from the spirit and scope of the present invention.

I claim:
 1. A process for recovering nickel in soluble form from aliquor, the liquor being obtained from a leaching or beneficiationcircuit for oxidized nickel-containing ore, the process comprising:(a)precipitating nickel from solution; (b) adding an inert particulatecarrier and a flocculent to the liquor to form flocs comprising nickelprecipitate, inert particulate carrier, and flocculent; (c) separatingthe flocs from the liquor; and (d) separating the nickel precipitatefrom the flocs.
 2. The process defined in claim 1, further comprisingpassing the nickel precipitate and flocculent through a filter or aconcentration system to recover the nickel as a filter cake.
 3. Theprocess defined in claim 1, wherein the precipitation step (a) comprisesadjusting the pH of the liquor to precipitate the nickel as anhydroxide.
 4. The process defined in claim 1, wherein the precipitationstep (a) comprises adding sulphur containing compounds to precipitatethe nickel as a sulphide.
 5. The process defined in claim 1, wherein theseparation step (c) comprises allowing the flocs to settle by gravityand separating the relatively clarified liquor from the flocs.
 6. Theprocess defined in claim 1, wherein the separation step (c) comprisesrecovering the flocs by a magnetite separator.
 7. The process defined inclaim 1, wherein the separation step (d) is carried out by agitating theflocs.
 8. The process defined in claim 1, wherein the inert particulatecarrier is selected from the group consisting of sand, alumina,magnetite, hematite, ilmenite and calcite.
 9. The process defined inclaim 1, wherein the flocculent is a polyelectrolyte flocculent.